Typically, the feeding behavior of fish is highly dependent upon a number of variables such as the time of year, time of day, water temperature, and the amount of sunlight, to name a few. Depending upon the particular fish that the fisherman is endeavoring to catch, any one or a combination of any of the above variables may effect the location under the water's surface at which the fish will be most inclined to feed. Since it is often impossible to predict with any precision the depth that the fish are feeding on any particular day without experimenting first with different lures, the fisherman is often compelled out of necessity to bring on the excursion many different lures designed to operate at different water depths in the hope of finding that one lure which the fish will respond to.
Given the impracticality and inconvenience of having to bring many different lures, necessitating trial-and-error techniques, each trial of which requires cutting and re-attaching the fishing line, to find the lure that works, fishermen have long strived to provide a single lure with multiple-depth capability. Responsive thereto, a variety of adjustable-depth fishing lures have been developed in an attempt to solve the aforementioned problems. For example, U.S. Pat. No. 3,973,350 issued to England discloses an adjustable-depth fishing lure in which a hydrostatic pressure-sensitive rotary piston assembly is used to manually adjust the pitch of the lateral fins, and then to level the fins when the desired depth, corresponding to a particular water pressure, has been achieved. Although this lure may be adequate for its intended use, the fact that the means to adjust the depth is located partially outside the body may make it susceptible to accidental changing of the pitch setting due to fish strikes, snags, or underwater debris.
Another example of a prior art method for providing adjustable depth capability to a lure is illustrated and described with respect to FIG. 1B of applicant's disclosure. This lure comprises a substantially rubber body on which are mounted two adjustable fins coupled together by a rattle chamber passing transversely through, and frictionally held by, the lure body. Though this lure may also be adequate for its intended purpose, it also is susceptible to accidental changes in pitch setting since the means to control this setting (e.g., the fins) are located external to the body. In addition, the fact that the lure body is made of rubber may shorten its useable life span and possibly degrade the frictional cooperation between the rattle chamber and body, especially if used in salt-water, thus making more difficult the maintaining of the pitch setting. Thus, none of the prior art referred to herein will accomplish the purpose of the present invention.
A primary object of the present invention is to fulfill the above-mentioned need by the provision of an adjustable-depth crankbait fishing lure. A further primary object of the present invention is to provide such a fishing lure which is efficient, inexpensive, easy to use, and easy to manufacture. In addition, it is a primary object and feature of the present invention to provide such a fishing lure which is less prone to an accidental changing of the depth selection due to a fish strike or snagging of the lure on underwater debris. Another object and feature of this invention is to provide more generally a system for turning one shaft through part of a rotation when another parallel shaft turns part of a rotation in the same direction of rotation. More specifically, it is an object and feature of this invention to provide such a system wherein the position of both shafts can be easily changed by manually turning one shaft, but incidental forces on the other shaft will not change the positions of the shafts. Other objects and features of this invention will become apparent with reference to the following invention descriptions.